In Order of Presentation: Ishaan Sandhu DannY Kang Arslan Qaiser Eric Otte Anuar Tazabekov Capacitive Rain Sensor for Automatic Wiper Control

Introduction Background Design Specifications Conceptual Design Proposed Design Solution Hardware Specifications Reflection

Ipod/MP3 GPS In-Dash DVD Player Safety Satellite Radio

Transmits/Receives IR Beams Expensive Inaccurate (False Readings) Uneven Sensing Area

Background Why Capacitive? Higher Accuracy – Less False Positives Smaller Size – Sleek Design Cheaper Fewer Components – Less Complex

Background Basics of Capacitive Sensors Three Main Types: Displacement Accelerometer Pressure Capacitance Fringe Fields Dielectric differences

FUNCTIONALITY Sense water through windshield Communicate with microcontroller Control Wiper System ACCURACY Differentiate between various objects Differentiate varying rain levels COMPATIBILITY Fit in existing housing (1250 mm 2 ) Mount via adhesive COST Cheaper than optical sensor Overall cost < $12

Conceptual Design Sensor Traces Not Your Typical Capacitor! Sensing Area – Copper Traces Designed for Base Capacitance ≈ 5 pF Creates E-field When AC Voltage Applied Objects Interfere with E-field – Change Cin Design Parameters: Size, Spacing, Pattern Dielectric Insulators are Vital!

Conceptual Design Capacitance Monitoring Circuitry Need Circuitry to Monitor the Capacitance Value of the Sensor Traces Possible Design: RC Multi-vibrator - Change in C = Change in Time Constant Better Alternative: Dedicated IC’s – Capacitance to Digital Conversion Interface to Microcontroller for Software Processing

Conceptual Design Microcontroller / Processor Inputs Capacitance Data from C-D IC Sensor Response to Rain Can Be Characterized Software Algorithms To Discriminate Rain from Others Varying Wiper Speed In Response to Amount of Rain Prototype – Microcontroller Production – Body Control Module

Proposed Design Solution Capacitance-to-Digital Converter Use Analog Devices AD7746 Measures 24-bit capacitance Accurate to the femto-Farad Built in temp and humidity sensor for auto-compensation AD7151 and AD7747 models can also be used

Proposed Design Solution Differential Sensor Trace Design Three Separate Traces Source Excitation Voltage Applied To Center Trace Two Differentially Connected Traces Test Results to Determine Best Design (spacing, patterns, etc)

Proposed Design Solution PIC18F4520 Microcontroller Why we chose the PIC: Variety of I/O Ports Easy to use interface C++ programming Free! Can compare voltages

Proposed Design Solution Power Supply and Requirements Prototype will use batteries (9V Batteries) Production Design will use car battery PIC needs steady 5V AD7746 (C-D) needs steady 5.6V Buck Converter Circuit

Proposed Design Solution PCB Layout Final design has two parts: Flex PCB: Sensor Traces Mounts via 3M Adhesive Standard 2-layer FR4 PCB: C-D Converter Microcontroller

Overall Design uses 3 layers Flex Layer – Capacitive Sensor C-D Converter ( AD7746 ) Buck Converter Circuit Microcontroller ( PIC18F4520 ) Wiper Switch

Part NameQuantityCost Analog Devices AD7151 Cap-to-Dig Converter 4$12.68 Analog Devices AD7745 Cap-to-Dig Converter 4$38.00 Analog Devices AD7746 Cap-to-Dig Converter 4$34.32 Analog Devices AD7747 Cap-to-Dig Converter 4$38.00 Analog Devices AD7746 Evaluation Board 1$ MP Adhesive8$42.40 Microcontroller1$0 Coaxial Cable Assembly3$57.08 Fabricate with Flexible PCB 2$ Total29$539.10

Background Design Specifications Conceptual Design Proposed Design Solution Hardware Specifications Questions?